Switched mode power supply driver integrated with a power transmission antenna

ABSTRACT

A driver comprising a switched mode power supply, wherein said switched mode power supply comprises an existing coil, the driver circuit further comprises: a first power transmission antenna ( 42 ) formed as a first coil which is either the existing coil of the switched mode power supply or coupled to the existing coil of the switched mode power supply, said first power transmission antenna ( 42 ) is adapted for being magnetically coupled to a second power receiving antenna ( 44 ) thereby forming a wireless power transmitter.

FIELD OF THE INVENTION

This invention relates to drivers with switched mode power supply.

BACKGROUND OF THE INVENTION

Sensors have been widely used in intelligent lighting control systems.For example, ceiling or wall mounted occupancy sensors can detectactivities within a specified area and send signals to a lightingcontroller. By doing this, the system can automatically turn lights onwhen someone enters an area or turn light off soon after the lastoccupant has left, to reduce energy use and provide added convenience.

Another example of intelligent lighting control is daylight harvesting,which concerns using daylight to offset the amount of electric lightingneeded to properly light a space in order to reduce energy consumption.This is accomplished by dimming or switching electric lighting inresponse to changing daylight availability in the space, which is forexample detected by a ceiling mounted light level sensor.

One major inconvenience of incorporating sensors in a lighting controlsystem is to establish the connections between the sensors and the lightpoints. Currently this is done in one of two ways.

A first method uses a wired connection between a sensor and a lightingcontroller which is either a central system controller or a distributedcontroller at the light point. This brings difficulties for retrofitapplications.

A second method uses wireless connections for easy retrofit. However,this adds complexity to the commissioning, i.e., pairing between sensorsand light points. To solve this, intelligent luminaires with integratedsensors have been developed in recent years.

For example, LED luminaires are known with integrated occupancy sensorsfor maximizing energy efficiency, and luminaires are known withintegrated motion sensors and daylight sensor. By using intelligentluminaires with built-in sensors instead of separately installedluminaires and sensors, the installation and commissioning costs oflighting control systems are reduced. However, this kind ofluminaire-integrated control also has disadvantages.

Firstly, the design complexity of the luminaires is increased. Differentsensors may have analog signals (e.g., a continuous voltage signal) ordigital signals output through different data interfaces (e.g., SPI andI²C used for digital sensors). This must be taken into consideration bythe luminaire manufactures when adding sensors into their luminaires.When it is necessary to replace an already integrated sensor with adifferent model (e.g., from a different supplier), redesigns aresometimes unavoidable.

Secondly, a lighting system using luminaires with built-in sensors haslimited flexibility. The sensor placement is tightly bound by theluminaire placement. For example, a storage room having luminaires withtemperature sensors may be redesigned into a meeting room. Thetemperature sensing function is no longer needed and occupancy detectionis instead required. The user has to replace the luminaire which isexpensive and inconvenient.

Thus, current intelligent luminaires with built-in sensors have thedisadvantages of high design complexity and low flexibility.

D1 EP2770804A1, D2 WO2009/029960A2, D3 US2011/057583A1 and D6US2012/080944A1 are all about wireless communication with lamps.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to the invention, there is provided a lighting unitcomprising:

a housing;

a light source arrangement within the housing;

a light source controller within the housing;

a first radio frequency antenna within the housing;

a second radio frequency antenna provided within or on the housing, forcommunicating with said first radio frequency antenna;

a contact interface at the outer surface of the housing which comprisesfirst contacts which are electrically connected to the second radiofrequency antenna; and

a reader circuit connected to the first radio frequency antenna, forprocessing signals received from said contact interface via said firstand second near field antennas.

This arrangement separates a circuit part and an antenna part of a radiofrequency sensor, such as a near field communication (“NFC”) sensor. Theantenna part is formed as part of the lighting unit housing (i.e. the“second radio frequency antenna”), whereas the circuit part is providedby the external sensor. This means that standard RF communicationprotocols (e.g. RFID) can be used by sensors which are physically(rather than wirelessly) electrically connected to the lighting unit.This provides a modular approach which enables different sensors to beused. The RF protocols enable the different sensors to be identified bythe lighting unit. In this way, the overall lighting system is easilyreconfigurable by simply selecting the desired sensor to be electricallyconnected to the lighting unit. The size of the antenna used by thesensor is not limited by the size of the sensor itself, and can belarger since it is formed as part of the housing of the main lightingunit. Similarly, the sensor can be made smaller and lower cost, so thata set of sensors can be available for use with the lighting unit, givingeasy and low cost reconfiguration options.

A modular approach is thus provided to enable an intelligent lightingunit with easily expandable sensing function. A passive or semi-passivesensor with a built-in NFC tag can be attached to the lighting unit toprovide connection to the antenna of the tag. The lighting unit thenreads the sensing data from the sensor via a built-in NFC reader. In thecase of a passive sensor, it harvests energy from the RF signal emittedby the NFC reader for both the sensing operation and the NFCcommunication. In the case of a semi-passive sensor with an internalenergy source such as a battery or solar cell, the energy source isprovided mainly for the sensing function.

By taking this modular approach, a number of sensors can be attached tothe luminaire as needed. The NFC (e.g. RFID) reader of the lighting unitcommunicates with the attached sensor which has only the chip part of aNFC (e.g. RFID) tag because the antenna for the NFC tag is part of thelighting unit.

The lighting unit may comprise a luminaire and the light sourcearrangement may comprise an LED arrangement. This provides a modularreconfigurable LED lighting system.

The second radio frequency antenna may be embedded in an outer wall ofthe housing and the contact interface is used for interfacing anexternal sensor. In this way, the second radio frequency antenna is asclose as possible to the tag part of the external sensor, and there is acontact interface for providing connection between them.

The lighting unit may further comprise a wireless power transmittermodule. This enables wireless powering of the external sensor as well asreading the sensor information, so that the sensor can be made as lowcost as possible. The wireless power transfer may in one example beachieved using the inductive coupling between the first and second radiofrequency antennae.

The lighting unit may further comprise a first power transmissionantenna within the housing connected to the wireless power transmittermodule and a second power receiving antenna provided within or on thehousing adapted to wirelessly couple with said first power transmissionantenna, wherein the contact interface further comprises second contactswhich are electrically connected to the second power receiving antenna.

This arrangement provides dedicated coupled antennae for data transferand for power transfer, so that the respective operations can beoptimized.

A light source driver may be provided which comprises a switched modepower supply. The first power transmission antenna may comprise a firstcoil or coils coupled with or placed in said switched mode power supply.

The first power transmission antenna may thus comprise a first coil orcoils either in parallel with a winding of the switched mode powersupply or else actually using a winding of the power supply. The secondpower receiving antenna may comprise a second coil or coils sharing acore or otherwise magnetically coupled with the first coil or coils.This arrangement for example makes use of an existing inductivetransformer used by the light source controller to implement thewireless power transfer.

The switched mode power supply may for example comprise a flybackconverter including a transformer which has a primary side winding and asecondary side winding, and said first coil or coils are in parallelwith the primary side winding and said second power receiving antennacomprises a second coil or coils magnetically coupled with the firstcoil or coils.

By providing a coil in parallel with the primary side winding, themagnetic field present in the inductive transformer is additionally usedfor wireless power transfer.

Alternatively, the first power transmission antenna may comprise theprimary side winding of the switched mode power supply and the secondpower receiving antenna may comprise a coil or coils spaced with saidprimary side winding so as to receive a leakage flux of the primary sidewinding. In this implementation, the transmit side of the wireless powertransfer transformer reuses an existing inductive winding to reduce thenumber of additional components needed.

The invention also provides a lighting system, comprising:

a lighting unit of the invention; and

an external sensor,

wherein the external sensor comprises a radio frequency tag, and acontact arrangement adapted to contact to the contact interface of thelighting unit, for connecting the tag to the contact interface and forcoupling the radio frequency tag to the second radio frequency antennaof the lighting unit.

The external sensor may comprise a power source so that the sensor canbe active (so that the power source provides all the required power forsensor operation) or it can be semi-passive (so that the power source isrecharged by power transfer from the lighting unit).

The external sensor may instead comprise a passive sensor. In the caseof a passive sensor, wireless power transfer from the lighting unit canbe employed, for example making use of the inductive coupling betweenthe first and second radio frequency antennae.

The invention also provides a lighting system, comprising:

a lighting unit of the invention; and

an external sensor,

wherein the external sensor comprises a radio frequency tag, a contactarrangement for connecting the tag to the contact interface, and awireless power receiver module,

wherein the contact arrangement comprises third contacts adapted toconnect to the contact interface of the lighting unit for coupling theradio frequency tag to the second radio frequency antenna and fourthcontacts for coupling the wireless power module to the second powerreceiving antenna.

This arrangement uses an external sensor with separate input forreceiving wireless power transfer and output for providing sensorinformation.

When the external sensor further comprises a rechargeable battery, asemi-passive approach is provided, with dedicated input for rechargingthe battery.

The sensor may for example comprise: a light sensor; or an occupancysensor; or a temperature sensor.

Based on the above embodiment of coupling the antenna with the switchmode power supply or using the existing winding of the switch mode powersupply, in another aspect of the invention, it proposes innovation inthe field of wireless power transfer. The inductive power transfersystem uses the principle of electro-magnetic induction, and two windingare electro-magnetically coupled together. One winding operates as apower transmitter and has power flowing through, the other winding wouldobtain inductive power and operates as a power receiver. A more detailedintroduction of the inductive power transfer can be found inUS20140232201A1.

In case of the inductively powering a load by a luminaire, a traditionalway is having two set of power system: one power system is for poweringthe lighting load and the other system is for powering the transmitterwinding/antenna. This needs separate components and the cost is high.

To better address this concern, the aspect of the invention proposes anintegration of a power transmission antenna with a switch mode powersupply of a driver, thus one power system can provide power for both theload and the power transmission antenna.

In an aspect, it provides a driver comprising a switched mode powersupply, wherein said switched mode power supply comprises an existingcoil, the driver circuit further comprises: a first power transmissionantenna formed as a first coil which is either the existing coil of theswitched mode power supply or coupled to the existing coil of theswitched mode power supply, and said first power transmission antenna isadapted for being magnetically coupled to a second power receivingantenna thereby forming a wireless power transmitter.

By re-using the existing coil of the switched mode power supply orcoupled to the existing coil of the switched mode power supply, thefirst power transmission antenna is integrated with the driver and theswitch mode power supply can power both the load and the powertransmission antenna. There is no need to use an extra power system forthe inductive power transfer, and the cost the saved.

In a further embodiment, the switched mode power supply comprises aflyback converter including a transformer which has a primary sidewinding and a secondary side winding. It should be understood that othertypes of switched mode power supply is also applicable for integratingthe power transmission antenna. For example, the power inductor of buckconverter, boost converter or buck-boost converter can also serve as thepower transmission antenna, or the power transmission antenna cancoupled to the power inductor so as to obtain power during the activepowering duration or during the passive freewheeling duration. Saidactive powering duration means the power source powers/charges the powerinductor, and said passive freewheeling duration means the powerinductor discharges/releases the charged power.

In a still further embodiment, said first coil is in parallel with theprimary side winding and said second power receiving antenna comprises asecond coil magnetically coupled with the first coil.

This embodiment gives a more detailed embodiment in which the powertransmission antenna is in parallel with the primary side winding, andcan obtain power from the power source directly.

In an alternative embodiment, the first power transmission antennacomprises the primary side winding and the second power receivingantenna comprises a coil spaced with said primary side winding so as toreceive a leakage flux of the primary side winding.

This embodiment re-uses the primary side winding as the first powertransmission antenna to transmit power via the leakage flux of theprimary side winding. Cost is further saved.

To provide enough leakage flux, a further embodiment provides animproved magnetic core for the transformer. Said core is magneticallyconductive at the inner side and has an air gap at the outer side, andthe outer side is adapted to couple an additional core on which saidsecond coil is winded. In this embodiment, the air gap can provideenough leakage flux.

In another embodiment, the first coil of the first power transmissionantenna coupled to an output terminal of the secondary side winding andadapted to receive power output from the secondary side winding.Alternatively, the first coil of the first power transmission antennacoupled to an output terminal of the flyback converter.

In this embodiment, the first power transmission antenna is moved fromthe primary side to the secondary side. Since the power output at thesecondary side can be regulated by the switch mode power supply, powerfactor and efficiency of the inductive power transfer can also beimproved.

In the above embodiment, the power on the first power transmissionantenna depends on the output of the secondary side winding. In case theoutput of the secondary side winding varies, the power for the inductivepower transfer also varies. To couple this issue and provide a constantpower on the inductive power transfer, the driver further comprises: atleast one additional coil in series with said first coil; at least oneshort circuiting switch, each of which in parallel with a respective oneof said least one additional coil; and a control circuit coupled to saidshort circuiting switch, for controlling said switch to short circuitthe respective additional coil, according to the power output by thesecondary side winding and the power required to be transmitted to thesecond power receiving antenna.

In this embodiment, the additional coil can act as power divider toadjust the ratio of the power on the first coil and the overall power.Thus in case the overall power output by the secondary side windingchanges, the additional coils can be switched in or out so as to keepthe power on the first coil constant.

In more details, the control circuit further comprises a sensing elementadapted to sense the power provided by said secondary side winding; andwherein said control circuit is adapted to: short circuiting the atleast one additional coil if the sensed power provided by said secondaryside winding is below a limit; or short circuiting the at least oneadditional coil if power required to be transmitted is above athreshold.

In this embodiment, when the output at the secondary side is too low,such as the driver is tuned/dimmed down, or when the inductive powertransfer needs extra power than normal, such as the second coil needs tocharge an extra battery, additional coils will be short circuited suchthat a larger ratio of power from the secondary side winding isdelivered to the inductive power supply.

In an alternative embodiment, the first power transmission antenna ismoved back to the primary side. More specifically, said flybackconverter further comprises: a freewheel loop coupled across the primaryside winding, said freewheel loop is adapted to freewheel the energy inthe primary side winding; and the first coil of the first powertransmission antenna is in the freewheel loop.

In current flyback converters, freewheeled energy is normally snubbed bya snubber circuit. In this embodiment, the freewheeled energy of theprimary side winding can be re-used in the first power transmissionantenna thus improves the power efficiency.

In a further embodiment, said freewheel loop comprises: a diodeforwarded from the current out-flowing end of the primary side winding;a capacitor between the diode and the current in-flowing end of theprimary side winding; and said first coil is in parallel with saidcapacitor.

This embodiment provides a more detailed circuit for utilizing thefreewheeled energy of the primary side winding.

In a further embodiment, said freewheel loop further comprises: aresistor in parallel with said capacitor and said first coil; and aswitch adapted to selectively switch either of the first coil or theresistor into the freewheel loop.

This embodiment can select either to transfer the freewheeled energy orto snub it.

In one example, said driver is for driving an LED arrangement. And theembodiment of the invention also provides a luminaire comprising adriver according to the above example and an LED arrangement driven bysaid driver.

Further, the embodiment of the invention also provides a sensor systemcomprising: a luminaire according to the above embodiment; and a sensorcomprising said second power receiving antenna. The sensor is poweredvia the inductive power transfer.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with referenceto the accompanying drawings, in which:

FIG. 1 shows a first example of lighting system with two possible typesof sensor;

FIG. 2 shows a second example of lighting system;

FIG. 3 shows an antenna coil arrangement;

FIG. 4 shows one possible circuit arrangement to provide powertransmission coils using an existing LED driver transformer;

FIG. 5 shows anther possible circuit arrangement to provide powertransmission coils using an existing LED driver transformer;

FIG. 6 schematically shows the transformer with a core to be used in theembodiment as shown in FIG. 5;

FIG. 7 shows the magnetic reluctance circuit diagrams of the transformerof FIG. 6;

FIG. 8 schematically shows the coupling between the second powerreceiving antenna with the transformer as shown in FIG. 6;

FIG. 9 shows the magnetic reluctance circuit diagrams of the transformerwith the second power receiving antenna of FIG. 8;

FIG. 10 schematically shows an embodiment for improving the coupling asshown in FIG. 8;

FIG. 11 schematically shows the topology of the driver with the firstpower transmission antenna in a freewheel loop at the primary side;

FIG. 12 schematically shows the topology of the driver with the firstpower transmission antenna at the secondary side.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a lighting unit having a light source controller,a first radio frequency antenna and a second radio frequency antenna allprovided within (or on) a housing of the lighting unit. A contactinterface at the outer surface of the housing comprises (first) contactswhich are electrically connected to the second radio frequency antenna.A reader circuit processes signals received from an external sensor whenthe sensor is electrically connected to the contact interface. Thisarrangement separates a circuit part and an antenna part of an RFsensor. The antenna part is formed as part of the lighting unit housingwhereas the circuit part is provided by the external sensor. This meansthat standard RF protocols (e.g. RFID or NFC) can be used by sensorswhich are physically (rather than wirelessly) electrically connected tothe lighting unit. This provides a modular approach which enablesdifferent sensors to be used.

FIG. 1 shows a block diagram of an example of the lighting system.

The system comprises a lighting unit 10 and a sensor 12 a or 12 b. Thelighting unit 10 has an outer housing 14 with a light source arrangement16 such as an LED arrangement within the housing. A light sourcecontroller 18 is within the housing.

An RF communication antenna 20 is provided within the housing and thisis part of a reader circuit 22, for example a near field communication(NFC) reader circuit. The NFC reader circuit can be a standard componentfor example as now frequency used in NFC smart phones.

A second radio frequency antenna 24 is provided within or on thehousing, for example embedded within the housing 14. This can also be anRFID or NFC antenna.

In the examples below, reference is made generally to near fieldcommunication (“NFC”) components, since the communication distances areshort and of the same order of magnitude as the dimensions of housing ofthe lighting unit. Typically, NFC systems are designed for communicationover distances of the order of centimeters, for example around 10 cm orless, and such communications systems can be employed for the wirelesscommunications in this system. RFID systems have a range which isdependent on the frequency used, and again it may be as low as 10 cm orless, or it may be much greater. The invention can be implementedgenerally using any radio frequency communications protocols, but thelow cost of short range RFID or NFC communications components makes themparticularly attractive for this application.

The first and second antennae 20, 24 communicate sensor data betweenthem.

A contact interface is provided at the outer surface of the housingwhich comprises first contacts 26 which are electrically connected tothe second near field communication antenna 24. The location of theantenna 24 is determined for an optimal communication performance withthe antenna of the NFC reader circuit 22.

The NFC reader circuit 22 is for processing signals received from theexternal sensor 12 a, 12 b when the sensor is electrically connected tothe contact interface.

The external sensor 12 a or 12 b comprises a tag part 30 which is thecircuit of the sensor, whereas the communication antenna of the sensor12 a or 12 b is the antenna 24. Thus, the antenna and tag chip areseparable by the electrical contact interface including the firstcontacts 26. The sensor has its own connector arrangement (comprisingcontacts 32) for connecting to the first contacts 26 of the lightingunit contact interface.

This approach provides modular design and enables an easily expandablesensing function. A passive or semi-passive sensor 12 a or 12 b with abuilt-in NFC tag chip (but no antenna) can be attached to the luminaireto provide connection to the antenna of the tag. The lighting unit readsthe sensing data from the sensor via its built-in NFC reader circuit 22.

FIG. 1 shows two possible examples of sensor.

The sensor can be a semi-passive sensor 12 a with an internal energysource 34 such as a battery or solar cell, which provides power mainlyfor the sensing function.

Alternatively, the sensor can be a passive sensor 12 b which receivesenough energy from the reader's RF signal for both the sensing functionand for communication.

In each case, the external sensor has a controller 36 and a sensingmodule 38. In the case of the passive sensor 12 b, there is power anddata communication between the controller 36 and the tag 30 as shown bythe two connections between the two units.

The controller is for example an ultra low power microcontroller unit(MCU) which communicates with both the sensing module 38 and the NFC tag30. For simple applications such as temperature sensing, thecommunication with the sensing module 38 can be realized by theprocessing unit of the NFC tag 30, thus eliminating the need of aseparate controller 36, and the control function is part of the tagitself.

The NFC tag 30 has two interfaces, a contactless interface to the NFCreader 22 in the lighting unit (by means of the antenna 24), and a wiredinterface to the controller 36 or the sensing module 38 if no separatecontroller is used.

In the case of the passive sensor 12 b, the NFC tag 30 can harvestenough energy through the connected antenna 24 from the RF field of theNFC reader 22 to power both the operation of the tag and the controllerand sensing module. Such NFC tags are widely available, for example theM24LR16E-R from STMicroelectronics is a NFC/RFID tag integrated circuitwith an I2C interface and an ISO 15693 RF interface, which can harvestenergy from RF signals emitted by NFC/RFID readers and convert into avoltage output to power other electronic components.

The NFC tag 30 is connected (by physical wires) to the contacts 32,which are used to attach the sensor to the lighting unit. When theexternal sensor is attached to the luminaire, i.e., the two connectorsare contacted, the NFC tag is linked to the antenna 24 embedded in orprovided on the cover of the lighting unit so that the tag is readableby the NFC reader 22.

Another benefit of separating the antenna 24 from the sensor tag, i.e.,putting the antenna in or on the cover of the luminaire, is thatsignificantly more area is available for the antenna meaning more energycan be harvested from the RF field.

The semi-passive sensor 12 a further contains an internal power source34, which could be a battery or an energy harvest device such as solarcell. The power source mainly provides energy to the controller 36and/or the sensing module 38. The NFC tag 30 can optionally use thepower source for sending the signal to the NFC reader 22 so that anenhanced communication performance can be achieved. The semi-passivesensor may optionally also use energy harvested by the NFC tag to powerthe controller or the sensing module to achieve an extended batterylife.

A further option is to increase the amount of the harvested energy tothe level that it can be used to charge the battery or directly powerthe sensor module and controller. In this way, a semi-passive sensor isturned into a passive sensor. This can be realized by using wirelesspower technologies such as inductive charging.

The functions of data communication and wireless power transmission canbe separated as shown in FIG. 2.

The same reference numbers are used for the same components and thedescription is not repeated. For completeness, an LED driver 17 is shownas a separate component to the LED source 16. The NFC reader 22 is alsoshown separate to the NFC reader antenna 20.

There are four antennae in the lighting unit 10. The first and secondantennae 20,24 provide data communication between the reader 22 and thesensor 12 c. A wireless power transmitter module 40 is added in thelighting unit 10. The wireless power transmitter 40 receives DC powerfrom the LED driver 17 to input an alternating current in a thirdantenna in the form of a power transmission coil 42. This generates amagnetic field between the power transmission coil 42 and a powerreceiving coil 44 (a fourth antenna) which induces a voltage in thepower receiving coil 44.

The wireless power transmitter 40 contains a driver circuit forregulating the current flowing through the power transmitter coil, and acontroller for circuit control and communication with wireless powerreceivers during power transmission. For example, there is control forstarting and stopping the power transmission, also for authenticationsuch as a compatibility check between the transmitter and receiver.

As for the NFC antenna 24 of the external sensor, the power receivercoil 44 may be embedded in the cover of the lighting unit and physicallyconnected (through wires) to the connector located on the outer surfaceof the cover. Thus, the lighting unit has a first power transmissionantenna 42 within the housing connected to the wireless powertransmitter module, and a second power receiving antenna 44 providedwithin or on the housing.

At the sensor side, a wireless power receiver module 50 is added whichcontains a rectifier for AC to DC conversion, a voltage conditioner(e.g., a DC/DC converter) for the delivery of a voltage with properlevel and characteristics to the load (e.g., the sensor module orbattery), and a controller for circuit control and communication withthe wireless power transmitter during power transmission.

The sensor has two sets of contacts 32,33 forming its contactarrangement and the lighting unit has two corresponding sets of contacts26,27 forming its contact interface. Thus, the lighting unit contactinterface comprises first contacts 26 and second contacts 27 which areelectrically connected to the second NFC antenna 24 and the second powerreceiving antenna 44 respectively. The sensor contact arrangementcomprises third contacts 32 and fourth contacts 33.

When the sensor is attached to the luminaire, i.e., all four contactsare contacted (as two connected pairs), the NFC tag 30 and wirelesspower receiver 50 are linked to the NFC antenna 24 and power receivingcoil 44 embedded in (or provided on) the cover of the lighting unitrespectively. This sets up not only the communication link between theNFC reader 22 and the NFC tag 30, but also the power transmission linkbetween the wireless power transmitter 40 and receiver 50.

If the sensor uses an internal rechargeable battery, then the wirelesspower receiver 50 will manage the charging of the battery. If no batteryis used, then the wireless power receiver will power the sensing module38 and the controller 36 directly.

FIG. 3 gives an example of how to arrange the NFC antennae 20,24 and thecharging coils 42,44 on a shared magnetic plate. The power transmit coiland the power receive coil are be tightly coupled to ensure an efficientwireless power transfer.

The coils for wireless power transmission can be implemented usingexisting coils, in particular coils which already exist as part of theLED driver circuits. For example a down converting transformer is oftenused as part of an LED driver.

FIG. 4 shows an example of reusing an LED driver with a typical flybacktopology.

The circuit comprises an EMI (electromagnetic interference) filter 60, arectifier 62 and a main down converting transformer 64 with a primarywinding 64 a and a secondary winding 64 b. A flyback circuit including amain switch and flyback diode is provided at the input side of thetransformer 64.

An additional coreless transformer 66 is added into the LED driver withits primary side winding, which functions as the power transmission coil42, connected in parallel with the primary winding 64 a of the maintransformer 64. In this way, the LED driver circuits can be reused toinput and regulate an alternating current to the primary winding 42 ofthe coreless transformer, thus eliminating the need for a separatedriver circuit for the wireless power transmitter 40. The secondary sidewinding of the coreless transformer 66 is the power receiver coil 44. Inthis example, the winding 66 comprises a coil or coils connected reversedotted with respect to the primary side winding. Therefore the secondaryside winding 44 of the coreless transformer is positioned outside of theLED driver, for example on the cover of the lighting unit in such a waythat a good space coupling with the primary side winding is achieved.

FIG. 5 shows another example of how to reuse a flyback LED driver to afurther extent.

The primary winding of the main transformer 64 of the LED driver isreused as the power transmission coil 42. The power receiver coil 44 isplaced with good coupling with the main transformer to fully utilize theleakage magnetic flux from its primary winding. This may require specialdesign of the main transformer 64 according to the requirements of boththe main lighting function and the wireless power transmission function.

FIGS. 4 and 5 show a typical constant current controlled flybackconverter. However, this is just one of many possible topologies ofswitched mode power supply which can be used within an LED drivercircuit. More generally, the first power transmission antenna can beformed as a coil which is either in the switched mode power supply (i.e.an existing coil of the switched mode power supply) or coupled to anexisting coil of the switched mode power supply. The second powerreceiving antenna is magnetically coupled to the first powertransmission antenna, and this may be across an air gap or a magneticmaterial.

To better elucidate the above aspect of the invention about theintegration of power transmission antenna with driver, the descriptionwould give more detailed embodiments and discussions.

Based on the embodiment of FIG. 5 wherein the primary side windingserves as the power transmission antenna, in order to provide enoughleakage flux, the embodiment as shown in FIG. 6 provides an improvedmagnetic core 60 for the transformer 64. The primary side winding 42 andthe secondary side winding denoted as 62 are winded on the core 60,wherein the core is magnetically conductive at the inner side and has anair gap 66 at the outer side. The core can be formed by oppositelyattaching two E-shaped half-cores together, wherein the middle leg ofthe E-shaped core is longer than the side legs. The arrows in the FIG. 6schematically show the magnetic flux.

FIG. 7 shows the magnetic reluctance circuit diagrams of the transformerof FIG. 6. Air gaps in transformer core increase the reluctance of themagnetic circuit, and enable it to store more energy before coresaturation. Magnetic reluctance is analogous to resistance in anelectrical circuit, but rather than dissipating electric energy itstores magnetic energy. Like the way an electric field causes anelectric current to follow the path of least resistance, a magneticfield causes magnetic flux to follow the path of least magneticreluctance. R₂ and R₃ represent the two air gaps of the proposedtransformer. Φ₁ is the magnetic flux of the magnetic field created bythe primary winding of the transformer. For the new transformer,magnetic energy is distributed among R₂ and R₃ and the sum of Φ₂ and φ³should equal to Φ₁.

FIG. 8 shows how an additional core 80, on which said second coil 44 iswinded, is coupled to the core 60. The outer side of the core 60 withthe air gap is adapted to couple an additional core 80 on which saidsecond coil 44 is winded. As the additional winding (the C-shape core)is put close enough to the transformer, it is coupled to the primarywinding of the transformer acting as an extra secondary winding. As theload of the additional winding, sensor can get energy wirelessly fromthe transformer.

FIG. 9 shows the magnetic reluctance circuit diagram of the transformersetup of FIG. 8. Due to the existence of the two air gaps (R₂ and R₃) onthe two side leg paths of the EE cores and the two newly created airgaps (i.e., R₄) in between the EE cores and the coupled C core, magneticfluxes are redistributed depending on the magnetic reluctance of eachpath. Φ₁ is still the magnetic flux of the magnetic field created by theprimary winding. The path of R₄-R₄ works as a parallel circuit to thepath of R₂ and R₃. Magnetic energy is redistributed among R₂, R₃ and R₄and the sum of Φ₂, Φ₃ and Φ₄ is equal to Φ₁.

The quantity of the magnetic flux flowing through the C-shape coredetermines the amount of energy transferring to the sensor. This can beadjusted by changing the size of the two air gaps between the EE coreand the C core. Larger gaps means larger magnetic reluctance (i.e., R₄)on the path leading to less magnetic flux flowing through, thereforeless power can be transferred.

It must be noted that the air gap between the transformer and theexternal core must be small enough to allow energy transfer. Too largemagnetic reluctance due to big air gaps will block the flowing ofmagnetic flux into the external core. In practical applications, thecasing of luminaires and sensors can easily reach 2 mm which is bigenough to block magnetic flux. This could be solved by embeddingmagnetic materials 100 in the casing to extend the allowed distancebetween the transformer and the external core, as illustrated in FIG.10. Using materials of different magnetic permeability has the sameeffect of adjusting the size of the air gap.

Back to the flyback converter as shown in FIG. 4, the diode and aparallel of a resistor and a capacitor, across the primary side winding64 a, is a loop that freewheels the energy in the primary side windingwhen the power switch turns off This loop is also known as snubber. Theembodiment of the invention proposes utilizing the freewheeled energyfor inductive power transfer, so as to save energy.

An embodiment of a luminaire 11 and an inductive power receiving deviceis shown in FIG. 11, wherein the luminaire comprises the driver with thefirst power transmission antenna Ls and the inductive power receivingdevice comprises the second power receiving antenna Rx. The powertransmission antenna Ls is in the freewheel loop, and is parallel andalternative with the snubber resistor Rs.

A relay controller 114, which could be an internal module of the flybackconverter or a separate module of the luminaire, keeps monitoring theexistence of external devices attached to the luminaire and controls therelay switch SWs accordingly. Normally, the relay switch SWs connectsthe resistor into the snubber circuit when there is no external deviceattached, so as to snubber the freewheeled energy in the primary sidewinding. When an external inductive power receiving device 12 ismechanically attached on the (casing of the) luminaire as illustrated inFIG. 11, the relay controller 114 detects this and controls the relayswitch SWs to connect the inductor Ls into the snubber. Various methodscould be used to detect the sensor, such as using a mechanicalstructure. The external inductive power receiving device 12 contains awireless power receiver module of which the second power receivingantenna, namely a coil Rx is coupled with the inductor Ls in snubbercircuit. The inductive power receiving device 12 may further comprises arectification and voltage/current correcting part 122 that converts thereceived power to a proper characteristic so as to power the load 124.

A zener diode Z_(s) connected in series with the diode D_(s) and theantenna Ls/resistor Rs to block the reverse voltage reflected from thesecondary side, so that only the freewheeled power is allowed to flowinto the capacitor C_(s).

The the capacitor C_(s) can further resonate with the inductor Ls suchas alternating current occurs on the inductor Ls and power istransferred.

It should be understood that the above resistor Rs, relay switch SWs andthe relay controller 114 are dispersible such that all freewheeledenergy can be directly transferred.

In above embodiments, the first power transmission antenna locates inthe primary side. The below embodiment would provide the first powertransmission antenna in the secondary side.

FIG. 12 shows a luminaire with a driver and an external power receivingdevice 12. As shown in FIG. 12, the first coil of the first powertransmission antenna 42 coupled to an output terminal of the secondaryside winding 64 b and adapted to receive power provided from thesecondary side winding 64 b.

As shown in FIG. 12, the driver comprises at least one additional coilL2 in series with said first coil 42, at least one short circuitingswitch SW, each of which in parallel with a respective one of said leastone additional coil L2; and a control circuit coupled to said shortcircuiting switch SW, for controlling said switch to short circuit therespective additional coil L2, according to the power output by thesecondary side winding 64 b and the power required to be transmitted tothe second power receiving antenna 44.

When the MOFSET switch is closed, the primary side winding 64 a isconnected to the input voltage source, namely the input capacitor. Thecurrent in the primary side winding and magnetic flux in the transformerincreases, storing energy in the transformer. The secondary winding 64 band the inductors 42 and L2 forms a closed circuit. The voltage inducedin the secondary winding is negative (at the upper terminal of secondside winding 64 b), so the rectifier diode is reverse-biased. Thenegative voltage generates a negative current in the closed circuit thatis from winding 64 b, ground, inductor L2, and power transmission 42,storing energy in the inductors L2 and 42. When the MOSFET switch isopened, the current of the primary side winding 64 a is stopped. Thevoltage of the secondary side winding 64 b reverses to become positive(at the upper terminal), forward-biasing the rectifier diode, allowingcurrent to flow from the secondary winding to the rectifier diode. Inthe mean time, there is a current flowing from the inductors L2 and 42to the rectifier diode. The energy from both the transformer core andthe two inductors recharges the output capacitor and supplies the load.Through the above two operations, if a second power receiving antenna 44is attached to the luminaire with its second coil 44 coupled with thefirst power transmission antenna 42, there will be wireless powertransmission from the antenna 42 to the second coil 44. The inductors 42and L2 is the output of the transformer to store energy during theMOSFET switch is closed and discharge energy to the load when the MOSFETswitch is opened. Adding of these inductors won't affect the normalworking of the flyback converter.

In an alternative embodiment, the first power transmission antenna canbe coupled to the output of the flyback converter, instead of to theoutput terminal of the second side winding. In this case, the powertransmission antenna 42 can be deemed as another load in parallel withthe LEDs load of the LED luminaire. The connection can be shown by thedash-dot line in FIG. 12, which is to the anode of the rectifier diode.

In the above embodiments, the power on the power transmission antenna 42depends on how much power the driver provides at the secondary side. Thedriver is normally controlled according to the LEDs' load requirement,and when the load requirement does not in accordance with the powerrequired to be transferred on the power transmission antenna 42, theexternal device 12 may not be powered properly. To address this concern,the embodiment uses the inductor L2, the switch SW and the controlcircuit comprising the resistor Rsense, the amplifier OP-AMP and thecomparator COMP.

The control circuit keeps monitoring the power requirement of the LEDload by measuring and amplifying the current of the resistor R_(sense)and comparing with a pre-set reference value REF. When the powerrequirement from the LED load is below a certain level, leading to theenergy in the inductor 42 is not enough to wirelessly power an attachedexternal device, the switch of the control circuit will be closed toshort-circuit L2 so that the more energy is allocated to 42. This way,more energy is available for transmitting wirelessly to the externaldevice. If the inductance of L2 is N times of the antenna 42, then theclosing of the switch will bring N times more energy to the antenna 42.

Alternatively, in case the external device needs a short-term largepower, such as to charge its internal battery or do excessivelypower-consuming operation, the switch of the control circuit will beclosed to short-circuit L2 so that the more energy is allocated to 42.

The inductance of 42 and L2 are chosen based on the parameters of theflyback converter, such as the output power, to properly allocate energyamong the two inductors so that they won't be saturated when theconverter is working at full its output power.

The embodiment of the invention can also be applied to other convertertypes. FIG. 13 shows an example wherein a buck converter is integratedwith the first power transmission antenna 42. As shown in detail in FIG.13, a first power transmission antenna 42 is in series with the existedpower inductor/coil I of the buck converter. A jumper J is placed inparallel with the power transmission antenna 42 and the jumper J is usedfor short circuiting the power transmission antenna 42 and forming thebuck loop, in case the power transmission is not needed. The powertransmission antenna 42 can receive power in either or both of the powerstoring phase and the power releasing phase of the power inductor I.

By way of first example, the sensor can be a low power temperaturesensor such as the LM20 of Texas Instruments (Trade Mark). When thepassive sensor is attached to the intelligent lighting unit, it cancommunicate through the NFC interface to provide the temperatureinformation. The controller in the lighting unit sends a request throughthe NFC reader to the passive sensor. When a request is received by thepassive through its NFC interface, the NFC tag in the passive sensorforwards the request to the sensor controller through its wiredinterface.

When a request is received by the sensor controller of the passivesensor, the the temperature data is extracted from the sensing moduleand this is written to the memory unit (e.g., EEPROM) of the NFC tag 30through the wired interface.

The NFC tag 30 sends the data stored in its memory unit back to the NFCreader 22 of the lighting unit through the NFC interface.

By way of second example the sensor can be a rechargeable batterypowered occupancy sensor such as The “OccuSwitch” (Trade Mark) ofPhilips (Trade Mark). When the sensor is attached to the intelligentlighting unit, energy efficient lighting control is achieved.

The wireless power receiver 50 of the sensor manages the charging of thebattery. When there is a need to charge the battery (e.g., the energylevel of the battery is below a threshold), it communicates with thewireless power transmitter 40 to start wireless power transmission.

The sensing module of the sensor keeps monitoring the activities in thespecific area and sends the status (i.e., occupied or empty) to thesensor controller 36, which then write the status in the memory unit ofthe NFC tag 30 through the wired interface.

The controller 18 of the lighting unit periodically reads the status ofthe activity through the NFC reader 22, which communicates with the NFCtag 30 of the sensor via the NFC interface. Based on the status ofactivity, the light source controller 18 turns on and off the lightsource.

As will be clear from the examples above, the external sensors may senseconditions relating to lighting, such as light sensors or proximitysensors. However, they may also sense conditions which relate to otheraspects of the control of the environment, such as temperature. Forexample, the lighting system may be part of an overall systeminfrastructure which provides intelligent sensing and control not onlyof lighting. The lighting system can be part of a larger network whichreports to a central system and receives instructions from that centralsystem.

In addition to coupling sensors to the lighting system, other devicescan be coupled simply for the purposes of charging them. Thus, thecontact interface on the housing can function as a charging dockingstation.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or an does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measured cannot be used to advantage. Any reference signs inthe claims should not be construed as limiting the scope.

1. A driver comprising: a switched mode power supply adapted to beelectrically coupled to a load (R_(load)) and provide power supply tothe load (R_(load)), wherein said switched mode power supply comprisesan existing coil, wherein said existing coil is a power inductor of theswitched mode power supply which power inductor has an active poweringduration and a passive freewheeling duration so as to provide powersupply to the load (R_(load)), the driver circuit further comprises: afirst power transmission antenna formed as a first coil which is eitherthe existing coil of the switched mode power supply or coupled to theexisting coil of the switched mode power supply, said first powertransmission antenna is adapted for being magnetically coupled to asecond power receiving antenna external to said driver and differentfrom the load (R_(load)), thereby forming a wireless power transmitter.2. A driver as claimed in claim 1, wherein the switched mode powersupply comprises a flyback converter including a transformer which has aprimary side winding and a secondary side winding, wherein saidsecondary side winding is electrically connected to the load (R_(load)).3. A driver as claimed in claim 2, wherein said first coil is inparallel with the primary side winding and said second power receivingantenna comprises a second coil magnetically coupled with the firstcoil.
 4. A driver as claimed in claim 2, wherein the first powertransmission antenna comprises the primary side winding and the secondpower receiving antenna comprises a coil spaced with said primary sidewinding so as to receive a leakage flux of the primary side winding. 5.A driver as claimed in claim 2, wherein the first coil of the firstpower transmission antenna coupled to an output terminal of thesecondary side winding and adapted to receive power provided by thesecondary side winding.
 6. A driver as claimed in claim 2, wherein thefirst coil of the first power transmission antenna coupled to an outputterminal of the flyback converter.
 7. A driver as claimed in claim 5,further comprising: at least one additional coil in series with saidfirst coil; at least one short circuiting switch, each of which inparallel with a respective one of said least one additional coil; and acontrol circuit coupled to said short circuiting switch, for controllingsaid switch to short circuit the respective additional coil, accordingto the power output by the secondary side winding and the power requiredto be transmitted to the second power receiving antenna.
 8. A driver asclaimed in claim 7, wherein the control circuit further comprising: asensing element adapted to sense the power provided by said secondaryside winding; wherein said control circuit is adapted to: shortcircuiting the at least one additional coil if the sensed power providedby said secondary side winding is below a limit; or short circuiting theat least one additional coil if power required to be transmitted isabove a threshold.
 9. A driver as claimed in claim 2, wherein saidflyback converter further comprises: a freewheel loop coupled across theprimary side winding, said freewheel loop is adapted to freewheel theenergy in the primary side winding; and the first coil of the firstpower transmission antenna is in the freewheel loop.
 10. A driver asclaimed in claim 9, wherein said freewheel loop comprises: a diodeforwarded from the current out-flowing end of the primary side winding;a capacitor between the diode and the current in-flowing end of theprimary side winding; and said first coil is in parallel with saidcapacitor.
 11. A driver as claimed in claim 10, wherein said freewheelloop further comprises: a resistor in parallel with said capacitor andsaid first coil; and a switch adapted to selectively switch either ofthe first coil or the resistor into the freewheel loop.
 12. A driver asclaimed in claim 4, wherein the transformer further comprises a core onwhich said primary side winding and said secondary side winding arewinded, wherein said core is magnetically conductive at the inner sideand has an air gap at the outer side, and the outer side is adapted tocouple an additional core on which said second coil is winded.
 13. Adriver as claimed in claim 1, wherein said driver is for driving an LEDarrangement.
 14. A luminaire comprising a driver as claimed in claim 13and an LED arrangement driven by said driver.
 15. A sensor systemcomprising: a luminaire as claimed in claim 14; and a sensor; saidsensor comprises said second power receiving antenna.
 16. A driver asclaimed in claim 1, wherein the switched mode power supply is adapted topower/charge the power inductor during the active powering duration andthe power inductor is adapted to discharge/release the charged power tothe load (R_(load)) during the passive freewheeling duration.